It is the abnormal forward movement of one vertebra over the vertebra below. Most often, this forward slip of the vertebra occurs in the lumbar area of the spine. This slippage and herniation of the disc causes pressure on the nerve roots associated with the affected vertebrae, causing pain and dysfunction. There are various types of spondylolisthesis.
Type 1 - Congenital spondylolisthesis
An individual is born with the abnormality of the posterior bony arch of the spine, which causes the slippage. This is usually seen at the L5-S1 level and often associated with abnormality of the facet joints. Patients usually present with back pain during the adolescent growth spurt. CT and MRI scans are required to diagnose the dysplasia (abnormal bone formation).
Type 2 - Isthmic spondylolisthesis
Isthmic spondylolisthesis is caused by a defect in a part of the bone called the pars interarticularis. The pars bone connects the upper joint of one vertebra to the lower joint. The defect is usually caused by a stress fracture in individuals with a hereditary predisposition (some minor abnormality or weakness of the pars at birth). In certain individuals a defect may exist without any forward slip, referred to as spondylolysis. This itself can be painful.
Type 3 - Degenerative spondylolisthesis
Degenerative spondylolisthesis is a forward slippage secondary to arthritis of the spine. Spinal stenosis is usually associated with this process. This is due to a long standing degenerative disc leading to weak facet joints in the back of the spine. This is usually seen at L4-L5 level.
In degenerative spondylolisthesis, surgery is indicated if slippage progressively worsens or if back pain does not respond to nonsurgical treatment and begins to interfere with activities of daily living. In the congenital and high dysplastic group, surgery is done at early stages to prevent neurological complications.